Facebook just launched a new messaging system, which is supposed to be an innovative, simple take on email.

CEO Mark Zuckerberg says, “it’s not email.” It’s a combination of IM, SMS, and email.

So it is email, just with a few extra features.

Here’s the three main points that Facebook says differentiates its new messaging service from traditional email:

* Seamless messaging: You can be reached easily anywhere anytime, be it email, SMS, or IM. You don’t have to email a friend, or IM a friend. You send a message and check the box to make sure it goes to the right place.

* Conversation history: All those conversations are in one long stream that looks like SMS or IM histories. So you can hold on to you all your messages for eternity. Instead of having some conversations on email, some on texts, some in IM, you get them all in one place.

* Social inbox: Facebook can give you good filtering based on your friends. You will get three options — messages, other, and spam. Messages will come from people that you’re friends with on Facebook. Other will be everything else. And spam is spam.

The service starts rolling out today to select users, and will go wider in the coming months. Facebook will give users @facebook.com email addresses.

Will this kill Gmail or Yahoo mail? Zuckerberg says he doesn’t think people will wake up one day and just shut down their Gmail or Yahoo account, but he does think this conversation format is the future. Gradually, he thinks (hopes?) people gravitate to Facebook’s system.

If you have any questions about Facebook’s new system, ask in the comments, and we’ll try to answer.